How I'm thinking about our house, transportation, food and waste, to minimize environmental impact, while improving quality of life and having fun.

12/18/2012

Window shades

One of the technologies I have tried in House 5 is insulating window shades with side tracks. I got four Ecosmart cellular shades from Gordon Clements at Gordon's Window Decor. One is translucent, and the other three are blackout shades, achieving that by using aluminum foil inside the cells. Because the foil is reflective to radiant heat transfer, these shades have a higher insulating value than the translucent version. They also have two rows of cells, to further increase insulating value. In cross section they look like this:

The side edges of the shades are slit and a plastic fin that is installed on the sides of the window opening runs in the slit and makes a rudimentary and simple seal. The bottom has a weatherstrip to seal to the window sill. Here's a close-up of the shade and side fin:

Here's a shade fully down:

And here it is with the top partially down, nice for daylight with some privacy:

So how do they work? Well, they definitely insulate - when opened in the morning a little puff of cold air drops out. And there is condensation on the glass, notably more than the unsealed, single row cellular shades we have elsewhere in the house. My colleague and friend Andy Shapiro did some careful measuring on one of his and calculates that the effective added R value is about R-4.

These shades aren't cheap, although they are a lot less money than a window replacement. If you have leaky windows, these won't solve that problem - they're not that air tight. A storm window will do a better job of sealing, but won't add as much insulating value. I think that if you are considering shades at all for privacy reasons, and have reasonably tight windows, an insulating shade such as these can make sense, and they handle fairly large windows well. We've noticed that the largest one, covering a triple window about 7 feet wide and 5 feet tall, is perhaps a bit too large for the hardware that rolls it up - we help it up with one hand as we retract it in the morning.

Putting the two shades in the living room down definitely makes that room more comfortable to be in, as the two largest windows in the house are on the east and south of that space, and it's where we spend a lot of time. The change in the radiant temperature is noticeable. So all in all we consider this to be a success as we've applied it here.

Comments

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I have these very same shades in my home. I too have a blackout shade over a large window bay and have experienced hardware that is stressed to handle the load. Additionally, I've discovered that one needs to be careful about leaving the blackout shade fully down on a sunny day. The window with the blackout shade faces South and the triple glaze windows have a SHGC of 0.45. The temperature between the window and shade has gotten warm enough to soften and distort the plastic side tracks!

I'd recommend the blackout shade for a average or small window as long as one is careful not to leave them down on a sunny day. The translucent shades have worked fine for even the large window bay we have it installed.

Thanks very much for sharing your experience, Dan. Great point about leaving the shade down. I think if I were to leave the house unoccupied I might try the shade down with the top lowered several inches - have you tried that, and if so, does it help?

The shades that we purchased don't have a top/down feature. Therefore, it's not an option for us to leave it open at the top. We have tried leaving 12 inches open at the bottom, however. I'm sure that's not as good as being able to leave it cracked at the top, but seems to do good enough as we haven't experienced the same problem as we did when fully closed.

Marc- I have been looking into these shades to install in a skylight and wonder if you have any concern about the condensation on the glass and whether that would eventually cause any mildew on the shade?
We're looking for something to block light from the skylight above our bed in our bedroom, and already when we wake up in the morning the glass is usually all fogged up (too much breathing?).

I reckon that leaving the shade down from the top still traps much of the cooler air between the window and shade, and an opening at the bottom lets the cold air drop and is replaced by room air. How much difference this makes, I don't know.

Hi Kate!
The skylight glazing gets colder for the same assembly due to night sky radiation, so I think it would be even more important to have a sealed edge assembly in a skylight. Whether there is enough condensation to actually drip I can't say.

Marc - We just installed several similar shades in our bedroom - my wife wanted the light blocked, and I was curious about blocking heat loss, but concerned about condensation.
The first few nights the condensation was really bad, but after talking with the supplier, we left the bottom of the shade slightly open to allow a little bit of air flow, which mostly solved the issue.

Obviously they are great for blocking light, but do you think the airflow needed to keep condensation down negates most of the insulating value of these things?

Yes, exactly right. So the next step is to measure the actual temp and RH in the bedroom and see if part of the issue is not enough ventilation in the room. Master bedrooms are worse, with two adults, than other rooms usually

Hi Marc: at R-4, I wonder if the Ecosmart window shades might provide one half of a solution for moveable night time window insulation. For decades inventors have contemplated coming up with an automated system for adding opaque window insulation in passive solar houses during night time. For example, a Zomeworks product blew styrofoam beads between two panes of glass then vacuumed them out during the daytime.
Have you ever heard of a timer controlled motorized mechanism which could pull an Ecosmart or similar window shade up in the early morning, then down at night fall? Could be possible cheap and easy retrofit solution for many R-2 windows in the existing housing stock.

Large scale motorized shades were around 30 years ago in the heyday of the passive solar days. In fact, one that South Mountain installed just recently failed after all that time! I expect that many shade manufacturers could fix you up with a motorized set-up. The Ecosmart shades have a fair bit of friction and occasionally jump the sidetrack, so i wouldn't try to motorize them without some re-design.

We installed some 60" tall triple cell fiber shades (no foil) from Smith Noble several years ago. I observe that the hanging weight of the shade material itself (the bottom rail is supported by the cords) causes the hex cells to stretch out vertically and pretty much collapse flat. This thins the shade substantially, especially in the upper part. S-N advises to pull the shades up all the way and leave for a day from time to time to restore the cell shape, but this is not very effective. What is your experience with the Ecosmart material in this regard? Does the foil stiffen the cells and resist collapse any better?

Hello Dodd
I don't see that effect - for one thing, there are enough rows of cells that even when fully extended they are hexagonal. And the side tracks provide friction that seems to keep the extension even along the length of the shade.

Thanks, Marc. That's helpful to know. I like the design of the Ecosmart side tracks - they look simple and reasonably effective, and all the better if they help maintain uniform cell geometry. The top/bottom "cordless" mechanisms on my current shades are not very durable (rapid cord abrasion and frequent breakage), so I will be replacing them over time. I appreciate hearing of your experience with your shades and the usefulness of your blog posts in general.